More than one million people are being resettled

There have been consistent rumours that the 185-metre-high (605 feet) dam, which entails the removal of entire villages to higher ground, is being shoddily constructed, amid reports of endemic corruption in the project.

But the China Daily report represents an usually frank admission that the dam has serious shortcomings and some leaders are now critical of the project.

"During the past three years, concrete placement in the project has not been first class, causing a variety of related accidents and drawbacks, though the concrete process has improved compared with previous years," Ms Qian was quoted as saying.

The cracks measure a maximum 1.25 millimetres across and 2.5 metres deep, according to China Daily.

The paper said cracks had also been found in the project's permanent ship-locks and ship-lifts.

Costly project

The Chinese Government's prestige project is hugely costly - officially it is expected to cost at least US$24bn but unofficial estimates say it could cost at least three times that amount.

China hopes the dam will stop devastating floods

It has been bedevilled by corruption. In 2000, 97 officials were convicted of embezzlement from the dam fund.

Activists have criticised the enforced resettlement of those whose homes lay in the 600 kilometre-long (375 miles) area, which will form the Three Gorges reservoir and the loss of many historic buildings and artefacts that will be drowned.

The dam is intended to control China's notorious flooding problem. But engineers have questioned whether the dam will be effective, citing problems with sedimentation and the construction itself.